Abstract: Seismic sensor systems and sensor station topologies, as well as corresponding cable and sensor station components, manufacturing and deployment techniques are provided. For some embodiments, networks of optical ocean bottom seismic (OBS) stations are provided, in which sensor stations are efficiently deployed in a modular fashion as series of array cable modules deployed along a multi-fiber cable.

Abstract: A method and apparatus for demodulation of detected fringes from interferometric sensors with high slew rates are provided. A detected interference signal may be mixed with a local oscillator phasor to obtain a mixed signal, the local oscillator being controlled to produce a frequency that roughly matches the fringe frequency of the interference signal. A sensor phase estimate may be obtained from the detected interference signal or the mixed signal. The local oscillator signal can be computed from the sensor phase estimate. The mixed signal and the sensor phase estimate may be low pass filtered and decimated and the resulting decimated mixed signal and decimated sensor phase estimate may be processed and combined with moderate processing power requirements in an effort to accurately measure the sensor phase for the interferometric sensor.

Abstract: Seismic sensor systems and sensor station topologies, as well as corresponding cable and sensor station components, manufacturing and deployment techniques are provided. For some embodiments, networks of optical ocean bottom seismic (OBS) stations are provided, in which sensor stations are efficiently deployed in a modular fashion as series of array cable modules deployed along a multi-fiber cable.

Abstract: Seismic sensor systems and sensor station topologies, as well as corresponding cable and sensor station components, manufacturing and deployment techniques are provided. For some embodiments, networks of optical ocean bottom seismic (OBS) stations are provided, in which sensor stations are efficiently deployed in a modular fashion as series of array cable modules deployed along a multi-fiber cable.

Abstract: Seismic sensor systems and sensor station topologies, as well as corresponding cable and sensor station components, manufacturing and deployment techniques are provided. For some embodiments, networks of optical ocean bottom seismic (OBS) stations are provided, in which sensor stations are efficiently deployed in a modular fashion as series of array cable modules deployed along a multi-fiber cable.

Abstract: Unwanted signal components in time-division multiplexed (TDM) systems may lead to crosstalk and noise if these pulses overlap with signal pulses from an interrogated sensor. The crosstalk and noise are dominated by interference between the signal pulses from the interrogated sensor and the unwanted signal components and can be greatly reduced by suppressing this interference signal. The unwanted signal components may include overlapping pulses originating from different sets of interrogation pulses (repetition periods). Modulating the phase or frequency between the repetition periods so that the unwanted interference signal does not appear at frequencies from which the phase of the interrogated sensor is demodulated suppresses this interference. Other unwanted signal components include leakage light during dark periods of the duty cycle of an interrogation signal.

Abstract: Seismic sensor systems and sensor station topologies, as well as corresponding cable and sensor station components, manufacturing and deployment techniques are provided. For some embodiments, networks of optical ocean bottom seismic (OBS) stations are provided, in which sensor stations are efficiently deployed in a modular fashion as series of array cable modules deployed along a multi-fiber cable.

Abstract: A method and apparatus that uses specific source modulation and detectors to detect a response that carries information about a system response matrix associated with each sensor in a interferometric sensor array and extracting a sensor response in a manner that eliminates polarization-induced signal fading and that is insensitive to lead fiber birefringence fluctuations.

Abstract: Unwanted signal components in time-division multiplexed (TDM) systems may lead to crosstalk and noise if these pulses overlap with signal pulses from an interrogated sensor. The crosstalk and noise are dominated by interference between the signal pulses from the interrogated sensor and the unwanted signal components and can be greatly reduced by suppressing this interference signal. The unwanted signal components may include overlapping pulses originating from different sets of interrogation pulses (repetition periods). Modulating the phase or frequency between the repetition periods so that the unwanted interference signal does not appear at frequencies from which the phase of the interrogated sensor is demodulated suppresses this interference. Other unwanted signal components include leakage light during dark periods of the duty cycle of an interrogation signal.

Abstract: A method and apparatus for producing depolarized light that is useful in forming interrogation signals for an optical sensor array and demodulator having reduced polarization-induced fading and phase noise. The depolarized light is produced by splitting a light beam, delaying a first orthogonal component of the light beam with respect to a second orthogonal component of the light beam using a predefined delay, while maintaining the polarization of the first orthogonal component and the polarization of the second orthogonal component. The delayed light beams are combined to produce a depolarized light beam by selecting a predefined delay that causes an interference signal having a delay equal to the predefined delay to be suppressed during a demodulation process.

Abstract: A method and apparatus that uses specific source modulation and detectors to detect a response that carries information about a system response matrix associated with each sensor in a interferometric sensor array and extracting a sensor response in a manner that eliminates polarization-induced signal fading and that is insensitive to lead fiber birefringence fluctuations.

Abstract: Fiber optic particle detector for measurements in a fluid flow, comprising an optical fiber (2,3,12) being acoustically coupled to a mechanical element (11,13,14) adapted to be acoustically coupled to the flow, a fiber optic interferometer (54,56) and a light source (12,51,55) providing light in said optical fiber.

Abstract: Method and assembly for sustained elimination or reduction of polarization induced signal fading in optical interferometer networks comprising at least two optical paths from an input port to an output port, the transmission delays of the paths differing by ?, an interrogation arrangement interrogating the optical phase differences between the paths, containing at least one optical source launching optical power into a port, a detector arrangement converting the optical power from an output port into electrical detector signals, and a control and signal processing unit capable of processing detector signals to determine the phase difference. The method comprising the steps of: altering the input polarization state produced by the source with a modulation frequency that is comparable to or higher than 1/(4?) receiving the optical signals at the detector arrangement providing a detector signal; processing the detector signal determining the phase difference between the optical signals.

Abstract: An optical waveguide Bragg grating fabrication apparatus (1) comprises a light source (2) providing ultra-violet (UV) light and optical means (4,5A-B,6A-B,7A-B,9) for adapting the light beam to form an interference pattern in a photosensitive optical waveguide (8). The interference pattern has a spatial intensity modulation along the length of the optical waveguide and thus providing an optical grating in the waveguide in the form of a refractive index modulation. The optical means comprises a movable non-uniform diffractive mask (4) for dividing the optical beam in at least two beams (12A-B) and optical elements for collecting two or more of the light beams to interfere on the optical waveguide. The optical means comprises position control means for controlling the position of at least one mirror or lens. Corresponding methods and the use of a super-periodic diffractive mask in such fabrication are described.